Shi'ite militiamen are everywhere. Police and Iraqi army checkpoints are nowhere in sight. US soldiers are keeping their distance. Sadr City - the Baghdad nerve center for the powerful Mahdi Army - is suddenly back on edge as the militia leader, Muqtada al-Sadr, and Iraq's government lock in a dangerous confrontation over clout and control among the nation's majority Shi'ites. The epicenter of the showdown has been the southern oil hub of Basra, where clashes have claimed dozens of lives this week and al-Sadr's forces face a Friday deadline to surrender. But a more finely tuned measure of the tensions may be found among the one- and two-story homes and shabby storefronts of Sadr City. As the crisis deepened, The Associated Press toured Sadr City on Wednesday to observe its rapid swing from relative quiet to a return of the Mahdi Army swagger before the US military troop buildup in Baghdad last year. Sadr City - named after Muqtada al-Sadr's father, who was assassinated in 1999 - is seen as critical to the overall stability and security of the capital. A resurgence of Mahdi Army attacks and opposition could roll back the gains that have allowed Baghdad residents to take cautious steps toward normal life and offered Washington hope of accelerating troop withdrawals. But recent days have resurrected old challenges. Al-Sadr's militia forces, estimated at about 60,000, now seem itching for a fight. The current crisis came to a head over US and Iraqi raids that have detained hundreds of Mahdi Army loyalists even as the group maintained a shaky cease-fire since August - which the Pentagon has credited for helping bring down violence. The tensions have spilled over into street battles in Basra between Mahdi fighters and Iraqi government forces. Fighting also has flared in other cities across southern Iraq's Shi'ite heartland - where Iran is hedging its bets by supporting factions of the Mahdi Army and its main Shi'ite rival. Mahdi fighters also are blamed for a series of rocket barrages on the US-protected Green Zone, which was hit again Wednesday. The Pentagon appears to want no part of the current troubles. Commanders worry that American troops could be drawn into difficult urban conflict, sapping energy from the fight against al-Qaida in Iraq and other Sunni insurgents. US forces have made only sporadic stabs into Sadr City, choosing instead to strengthen a security cordon on the outskirts. US commanders, meanwhile, have a limited presence in southern Iraq and show no signs of diverting soldiers - as they did in the last major fight against the Mahdi Army in 2004. "We are a different force than the one you saw in 2004," a senior Mahdi commander said at his Sadr City home. "We are now better organized, have better weapons, command centers and easy access to logistical and financial support," added the commander, who spoke on condition of anonymity because he is not authorized to speak to the media. Squatting on the floor next to two of his fighters, the commander sipped sweet black tea as a US helicopter flew low overhead. A burst of gunfire rang out at one point. Another moment, he listened to the screech of a rocket. "That's going to the Green Zone," he said. When one of his fighters left the house, he warned about driving too close to American patrols on the edge of the district - a grid-pattern of teeming streets in northeast Baghdad built in the 1950s to house poor Shi'ite workers. It was first named Revolution City. Then it became Saddam City. After Saddam Hussein's fall in 2003, it was designated Sadr City after al-Sadr's father, Mohammed Sadeq al-Sadr, whose death is blamed on Saddam agents. "Don't be too impressed with what the Americans have. We can still win because we have faith and a just cause on our side," said one of the two militiamen in the commander's home. Sadr City, home to 2.5 million people, looked like a place bracing for battle. Its streets - normally crowded and noisy - were oddly quiet. Besides the militiamen, only youngsters were out in large numbers, playing soccer on dirt fields. Most stores were shuttered. The militiamen, some wearing ammunition belts and sporting two-way radios, were out in full force dressed in a ragtag collection of tracksuits, jeans and pajamas. But they carried the essential firepower for effective street conflict: AK-47 rifles or grenade launchers. Some stood behind rickety market stands with machine guns perched on top. Snipers took up position on rooftops. Others drove in pickup trucks fitted with machine guns. Many curbs showed traces of disturbed asphalt - usually a telltale sign of freshly planted roadside bombs. Streets were barricaded by rocks, metal furniture or burning tires. Lookouts on motorbikes relayed the latest movements of US armor deployed nearby. Mahdi Army commanders have told the AP that the militia has recently taken delivery of new weapons supplied by backers in Iran. The arsenal, they said, included roadside bombs, anti-aircraft guns and Soviet-designed Grad rockets. They also said an infusion of cash, also from Iran, helped the militia set up new command centers equipped with Internet-linked computers, fax machines and satellite mobile phones. They have also received global positioning system devices, they said. The United States has long accused Iran of providing Shi'ite militias in Iraq with arms and training. Iran denies it. Aides to al-Sadr in Baghdad insisted the Mahdi Army cease-fire remained in force, but warned of dire results if Prime Minister Nouri al-Maliki's government continued its crackdown against Mahdi militiamen. "There will be grave consequences," said Sheik Salman al-Feraiji, al-Sadr's chief representative in Sadr City. "We are not going to stand by and watch our sons getting killed," he told tribal leaders at a mosque. "You must tell the government that you will disown it if it doesn't stop the operations in the entire south." Al-Sadr's movement gained ground in Sadr City in the immediate aftermath of Saddam's ouster. It quickly filled the vacuum left by the regime's fall - and Washington's lack of postwar planning - by running basic services and clamping down on looting in a district that had once been notorious for high crime and unemployment. The militia is not universally popular in Sadr City because some of its men are involved in extortion and kidnapping. But the Mahdi Army is credited by most residents for protecting the district against Sunni militants during the height of Baghdad's sectarian war in 2006 and early 2007. The bond between Sadr City's residents and the militia was on display Wednesday, with families offering fighters water, tea and food. "Today, a family sent us rice and meat for lunch," said another militia commander, who identified himself only by the nickname Abu Ali and said he was one of 12 who oversee the Mahdi Army operations in Baghdad and the south. Al-Sadr's support was instrumental in helping al-Maliki clinch the prime minister's job in 2006, but the two men fell out about a year ago. "Down with al-Maliki's government," is now common graffiti in Sadr City. "The Dawa party is treasonous," declared another one, referring to al-Maliki's party.